ENERGY-TRANSFER BETWEEN 2 MOBILE CHROMOPHORES IN A ZERO-ENERGY TRANSFER CONFIGURATION - CROSS-CORRELATION EFFECTS IN THE FLUORESCENCE ANISOTROPY R(T)

The energy transfer process between a pair of mobile chromophores has been determined by solving the stochastic Liouville equation numerically. The configurations of the chromophore pair were chosen in such a way that for the static case the energy transfer rate is zero. A restrictive molecular reorientation diffusion model is introduced in order to describe the reorientation of the chromophores. This motion introduces a fluctuating dipole-dipole coupling between the chromophores, and thus opens the energy transfer control channel. We observe no qualitative difference between the relaxation behaviour of the time-correlation function (CHI1(t)CHI1(0)) in the strong coupled or slow motion regime and the weak coupled or perturbation regime. (CHI1(t) refers to the probability that the initially excited chromophores remains excited at time (t.) This finding may introduce a serious complication when intermolecular distances are extracted from fluorescence anisotropy measurements. The absence of cross-correlation effects between the energy transfer process and molecular reorientation in the fluorescence anisotropy correlation function is also analysed in detail.